1. Field of the Invention
The present invention relates to a photographic support and a photographic material, more specifically to a photographic support comprising a biaxially stretched polyester film which is excellent in transparency and mechanical strength and is reduced in roll set curl, and a photographic material using the same, and particularly to a photographic support which does not have coating faults in providing a subbing layer and a back layer, which are liable to occur by heat treatment carried out on a roll for reducing roll set curl, and a photographic material using the same.
2. Related Art
In light of convenience in carrying and easiness in handling, further miniaturization is desired to cameras and in promoting the miniaturization, a storage space for a photographic film to be loaded has to be indispensably compact. Usually, a photographic film in which a roll film has been wound on a spool is loaded, and therefore the thickness of the photographic film itself has to be reduced in order to make the space therefor compact and secure a fixed number of photographing sheets (for example, 36 photographing sheets). In particular, a triacetyl cellulose (TAC) film which is a support for a photographic film has a thickness of an extent of 120 to 125 .mu.m even at present and is pretty thick as compared with the thickness (extent of 20 to 30 .mu.m) of a light-sensitive layer provided thereon. Accordingly, a reduction in the thickness of this support is considered the most effective means for reducing the total thickness of the photographic film. On the other hand, since a TAC film has intrinsically a weak mechanical strength, the smaller thickness than existing one reduces the strength, and therefore if the support has a film thickness of 100 .mu.m or less, edge folding occurs at a perforation part at both ends of the film when developing a light-sensitive material using it in a cinema type development treating machine, so that it has not stood practical use.
On the other hand, a polyethylene terephthalate (PET) support has so far been known as a support and used for X-ray films and plate making films. A PET support has an excellent strength and therefore is considered to be applied to a color negative film as well. However, while the PET support has an excellent strength, it has as low glass transition temperature as about 70.degree. C. and therefore has heavy roll set curl formed when the film is stored over a long period of time in a wound state under a high temperature atmosphere at about 60.degree. C. corresponding to the storage conditions in the summer season. Accordingly, the PET support has the defects that it is inferior in roll set curl and a handling property in a processing machine before development processing and has such inferior roll set curl removability that the roll set curl is scarcely removed after the development processing, so that it has not stood practical use.
On the other hand, known in Japanese Provisional Patent Publication No. Hei 6-35118/1994 and 6-35115/1994 are light-sensitive materials using polyethylene naphthalate which has been less liable to have roll set curl by subjecting a polyester film to heat treatment (hereinafter referred to as annealing treatment, for short, AN) at a temperature of the glass transition temperature (Tg) or lower in a wound state in order to improve the roll set curl after processing.
It is well known, however, that when various films including polyethylene terephthalate films are heated to the vicinity of Tg's thereof, the elastic moduli are suddenly reduced. Accordingly, if a thermoplastic resin film is subjected to heat treatment in the vicinity of a Tg thereof over an extended period of time under the condition that a large load is applied, the film does not stand the load, so that crinkles, folding and pressing are produced. Even if such faults on the surface are so fine that they can not be seen with eyes, it results in visible coating fault and inferior flatness of the film by subsequent coating steps for a subbing layer and a back layer. Accordingly, the existing film is that it can not stand use in a photographic support.
On the other hand, a light-sensitive layer of a photographic film contains gelatin as a component and has a weaker strength than that of a polyethylene terephthalate film. In addition thereto, a film containing polyethylene naphthalate disclosed in the publications mentioned above has intrinsically a strong strength and is liable to be cut in the form of delamination. Accordingly, the film has such a remarkably inferior cutting property that when the film is cut and processed to the form of a finished product after providing light-sensitive layers on this film, brought about is the problem that a cutting direction in cutting the film is deviated from a running direction of cracks caused in cutting to cause peeling and cracking of the light-sensitive layers, so that it has not stood practical use.